Process for the production of difluoromethane

a technology of difluoromethane and vapor phase, which is applied in the direction of physical/chemical process catalysts, halogenated hydrocarbon preparations, metal/metal-oxide/metal-hydroxide catalysts, etc., can solve the problems of low product yield and selectivity of the process for hfc-32 production

Inactive Publication Date: 2005-01-18
ALLIED SIGNAL INC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

Alternatively, a continuous recycle stream of the high boiling fraction obtained in step (C) is recycled to step (A) in which case a large excess of HF to organics is used. In the process of this invention, the higher the HF: organics mole ratio, the higher the yield and selectivity for HFC-32. Correspondingly, a large excess of HF will result in the reduction of HCFC-31 produced as well as the concentration of unreacted HCC-30. Additionally, the use of a large excess of HF will decrease catalyst deactivation rates and result in less decomposition in preheaters and vaporizers, especially when the reaction is conducted at pressures in excess of 3 atmospheres. Generally, a ratio of HF to HCFC-31, as measured after separation of HFC-32 from the product stream, of at least about 25:1 to at least about 300:1, preferably at least about 50:1 to at least about 200:1, and more preferably at least about 75:1 to at least about 150:1 is used.

Problems solved by technology

In practice, these processes for HFC-32 production suffer from a variety of problems including low product yield and selectivity as well as operational difficulties such as feed decomposition.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

examples 1 and 2

In a ½ inch Monel pipe reactor, about 110 ml Cr2O3 / Al2O3 (40 / 60 wt %) co-extruded catalyst were packed. The catalyst was dried / calcined at about 400° C. for about 16 hours using air at 2-3 liters per minute. Then, the temperature was lowered to 200° C. and air was replaced with nitrogen at about 0.5-1.5 liters per minute. Anhydrous HF was pumped into the reactor at about 1-2 ml / min until exotherm passed through the reactor. Subsequently, temperature was raised at 25° C. every half hour until the temperature was about 350-400° C. and held there for 8 hours. Temperature was then lowered to the desired reaction temperature. HF and HCC-30 were fed into the reactor at a molar ratio of 4:1 (HF: HCC-30). The mixture of HF and HCC-30 passed through two preheaters, the first of which was at about 100-185° C. and the second at about 200-275° C. The pressure was 50 psig and reactor temperature was 275° C. for Example 1 and 300° C. for Example 2. For Example 1, contact time was 16 seconds resul...

examples 3-6

In the pipe reactor of Examples 1 and 2, about 100-110 ml Cr2O3 / Al2O3 catalyst of 78 / 22 weight percent ratio was packed. The catalyst was dried / calcined and HF-treated using the same procedure as for Examples 1 & 2. HF and HCC-30 were fed into the reactor at a 4:1 (BF / HCC-30) ratio. A mixture of HF and HCC-30 was passed through the same preheaters indicated in Examples 1 & 2. Pressures, contact times, and the results are shown on Table II.

TABLE IIExample 3Example 4Example 5Example 6CatalystCr2O3 / Al2O3Cr2O3 / Al2O3Cr2O3 / Al2O3Cr2O3 / Al2O3(78 / 22 wt %)(78 / 22 wt %)(78 / 22 wt %)(78 / 22 wt %)Pressure (psig)50200225225HF / CH2Cl2 4444mole ratioTemperature275275275275(° C.)Contact Time11364026(sec)Conversion71707061(% CH2Cl2)Selectivity:HFC-3282818177HCFC-3118191923HCC-400.050.050.050.05Productivity(lbs / hr / ft3):HFC-3212121215

example 7

A 4 inch diameter Monel 400 reactor was charged with 4 liters of chromium oxide catalyst. The catalyst was dried under 20 slpm nitrogen flow at a temperature of 350° C. for 8 hours. After reducing the catalyst bed temperature to 250° C., anhydrous HF was added to the flowing nitrogen at a flow rate of 0.2 lbs / hr. The HF flow rate was gradually increased to 1.0 lb / hr and the temperature increased to 350° C. and held for 4 hours. The catalyst bed temperature was then decreased to 250° C. and chlorine introduced to the HF / N2 mixture at a rate of 500 sccm for a period of 24 hours.

After this pretreatment procedure, the chlorine and nitrogen flows were discontinued and HCC-30 was mixed with HF and passed though a preheater at 185° C. The vaporized HCC-30 and HF mixture was fed to the reactor at a pressure of 45 psig. the effluent from the reactor was quenched using a heat exchanger and fed into a distillation column maintained at 50 psig. The low boiling distillation components, HCFC-31, ...

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Abstract

The present invention provides a vapor phase process for the production of difluoromethane, HFC-32. The process of this invention provides for the preparation of HFC-32 by a process that exhibits both good product yield and selectivity.

Description

FIELD OF THE INVENTIONThe present invention relates to a vapor phase process for the production of difluoromethane, HFC-32. In particular, this invention provides a process for the preparation of HFC-32 that exhibits good product yield and selectivity.BACKGROUND OF THE INVENTIONIt is well known in the art that HFC-32 may be used as a replacement for environmentally disadvantageous chlorofluorocarbon refrigerants, blowing agents, and aerosol propellants. A variety of methods for the vapor phase production of HFC-32 are known.For example, U.S. Pat. No. 2,745,886 discloses a vapor phase process for fluorinating a variety of halohydrocarbons including methylene chloride, HCC-30, which process utilizes a hydrated chromium fluoride catalyst activated with oxygen. Similarly, U.S. Pat. No. 2,744,148 discloses a halohydrocarbon fluorination process in which an HF-activated alumina catalyst is used.U.S. Pat. No. 3,862,995 discloses the vapor phase production of HFC-32 by reacting vinyl chlori...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): C07C17/00C07C17/20C07B61/00C07C17/383C07C19/08B01J23/26
CPCC07C17/206C07C19/08C07C17/20
Inventor CLEMMER, PAUL GENESMITH, ADDISON MILESTUNG, HSUEH SUNGBASS, JOHN STEPHEN
Owner ALLIED SIGNAL INC
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